Catheter-based intravascular procedures typically require insertion of a vascular dilator followed by an introducer sheath. A conventional vascular introducer sheath 10, as illustrated in FIG. 1, has a vascular crossing profile, or diameter, necessarily wider than the accompanying vascular dilator 12, such that the dilator can be later retracted through the introducer sheath. This excess crossing profile of the introducer sheath is known to interfere with smooth advancement of the introducer sheath into a target blood vessel 14 or other chamber, and is known to cause tears in the target blood vessel, more commonly at or near the “trailing edge” 18 of the sheath 10, which refers to the portion of the distal end of the sheath that enters the vessel last when the device is inserted at an angle to the vessel, as in typical use. The “leading edge” 20 of the sheath 10, on the other hand, refers to the portion of the distal end of the sheath that enters the vessel first.
FIG. 2 shows an exemplary torn opening 16 in a vessel 14 caused by unequal crossing profiles of a conventional dilator 12 and introducer sheath 10, as well as a desired entry opening 22 having a smooth elliptical shape. As shown in FIG. 3, similar problems, such as puckering and tearing, can also occur during direct transthoracic or direct transmyocardial entry into the heart through a heart wall 24, such as for prosthetic heart valve implantation. The excess crossing profile in conventional intravascular systems is driven by the finite thickness of the wall of the introducer sheath, the limited flexibility of the introducer sheath, the required rigidity of the vascular dilator, and the requirement to withdraw the vascular dilator proximally through the sheath after delivery. Large-bore introducer sheaths, such as for structural heart interventions, tend to be necessarily thicker and more rigid and exacerbate these problems.